The present invention relates generally to printing in image forming systems, and specifically relates to pressure members in such systems.
Conventional image forming systems, such as toner imaging systems, where a latent charge image is developed with a pigmented toner before being transferred to a substrate, such as a sheet of paper, are widespread in the office and home. The latent image is formed on an imaging member with a charge-emitting device, and then developed with the toner. The developed image is ultimately transferred to the substrate to form a printed image.
Many technologies exist for forming a latent charge image, including optical image projection onto a charged photoconductive belt or drum, charging a dielectric member with an electrostatic pin array or electron beam, and charge projection from an ionographic print cartridge or from a plasma generator. Once a latent image is formed by any of these methods, the image may be developed with a toner before transferring the image to the substrate.
The developed image is transferred from a transfer member to the substrate. In some image forming systems the imaging member is also the transfer member, which transfers the developed image directly onto the substrate. In other image forming systems, the imaging member first transfers the developed image to a distinct transfer member, which then transfers the developed image to the substrate.
In general, there are at least three methods of producing the final image on a substrate. In the heating method, the toned image is heated to dry or fix the image on the substrate during the final stage of printing. In the transfusing method, the toned image is simultaneously transferred to and fixed on the substrate in a melted or fused state. By controlling the temperature, the relative tackiness, or the self-adherence of the heated toner, may be made to vary to achieve optimal transfer of the image. Finally, in the transfixing method, the final image may be produced by applying pressure, instead of heat, on either side of the substrate to transfer the image from the transfer member to the substrate. This pressure may be applied with a heavy pressure roll. Other methods of producing the final image on the substrate may include a hybrid of these methods, where, for example, some heat and pressure may be applied to transfer the image.
In the aforementioned methods of producing the final image on a substrate, pressure members, such as pressure rolls, can play an important role. The substrate is sandwiched between the transfer member and a pressure member at the transfuse nip. The transfer member applies a force to one side of a substrate while the pressure member applies a force on the opposite side of the substrate, thereby facilitating the transfer of the image from the transfer member to the substrate. The pressure exerted by the pressure member can exceed 2000 lb/in2 to effectively transfer the image onto the substrate. The pressure member should ideally be able to withstand these high pressures, and be rigid in order to apply this pressure evenly.
To withstand the high pressure, and provide rigidity, the pressure member can weigh upwards of 40 lbs., and be composed of a metal or alloy, such as an aluminum alloy or steel. Despite the strength of the constituent materials of the pressure member, however, the surface of the pressure member can be damaged by, for example, wrinkled paper passing through the transfuse nip. This type of damage is more likely when the substrate is a continuous web instead of a cut sheet. When the web mistracks, wrinkles can develop in the paper. These wrinkles can cause permanent deformation of the pressure member due to the high pressure, thus impairing printing quality.
To solve the aforementioned problems, a pressure member having a sleeve is provided suitable for use in an image forming system. The pressure member includes a core surrounded by the sleeve. The inner perimeter of the sleeve is larger than the outer perimeter of the core to enable the sleeve to be removed and replaced easily when worn out. Replacing the sleeve, instead of the entire, and much heavier, pressure role facilitates the maintenance of the image forming member, and reduces costs.
In particular, a pressure member suitable for use in an image forming system is provided. The member includes a core, and a sleeve removably and replaceably disposed around the core. The core may have an outer perimeter, and the sleeve may have an inner perimeter such that the inner perimeter of the sleeve is larger than the outer perimeter of the core to permit the sleeve to be removed from the core and replaced by a new sleeve. The inner perimeter of the sleeve may be about 2% larger than the outer perimeter of the core. At least one of the core and the sleeve may be formed of a metallic alloy, such as steel and/or aluminum alloy.
The core may include a cylinder and the sleeve may include a coaxial cylindrical shell disposed around the cylinder of the core, the inner circumference of the cylindrical shell being larger than the circumference of the cylinder of the core. The core may further include a flange formed at one end thereof to prevent the sleeve from separating from the core at that end.
Also provided below, suitable for use in an imaging forming system, is a pressure member including a core having a periphery, and a sleeve disposed about the core in intimate facing contact with only a portion of the periphery of the core, thereby allowing removal of the sleeve from the core.